The two-time Australian Open quarterfinalist was given a special clearance to board one of the flights from Los Angeles to Melbourne despite testing positive to COVID-19 in November and again on Monday.
For two nights in a row, Roger Federer came back from the jaws of defeat to inch closer to his seventh Australian Open title and an unprecedented 21st major.
The No. 58-ranked Chung is the first Korean player to reach the last four of a major, and the lowest-ranked man to reach the Australian Open semifinals since Marat Safin in 2004.
The 58th-ranked Chung relentlessly attacked Djokovic - who is playing his first tournament since Wimbledon because of an injured right elbow - in the 7-6 (4), 7-5, 7-6 (3) fourth-round win.
The 26-year-old American, who entered the season's opening major ranked 97th, missed a match point in the fourth set but held on for a 6-2, 4-6, 7-6 (4), 6-7 (7), 6-3 win over fifth-seed Thiem.
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